Question

我有以下表格：

CardsTable:
-------
CardID int
PersonID int
Number int
-----------------------
CardID    PersonID    Number
  1          10         22
  2          10         22
  3          11         24
  4          11         24
  5          10         22

对于具有相同ID的所有Number field，

personID应该是唯一的。

Following example is invalid:

 CardID   PersonID    CardID
    6         11         22   
    7         12         22
    8         12         24

如何使用条件唯一约束来实现它？

Answer 1

您可以使用具有用户定义函数的检查约束：

首先，创建函数：

CREATE FUNCTION dbo.CheckCards
(
    @PersonId int,
    @Number int
)
RETURNS bit
AS
BEGIN

IF EXISTS
(
    SELECT 1 
    FROM CardsTable 
    WHERE PersonId = @PersonId 
    AND Number <> @Number
)
BEGIN
    RETURN 1
END
RETURN 0

END

GO

现在，创建并填充样本表：

CREATE TABLE CardsTable
(
    CardID int,
    PersonID int,
    Number int,
    CONSTRAINT ck CHECK (dbo.CheckCards(PersonId, Number) = 0)
)

INSERT INTO CardsTable VALUES
(1, 10, 22),
(2, 10, 22),
(3, 11, 24),
(4, 11, 24),
(5, 10, 22)

然后测试检查约束：

BEGIN TRY
   INSERT INTO CardsTable VALUES (3, 10, 24)
   SELECT 'Success' As [Insert]
END TRY
BEGIN CATCH
    SELECT 'Failed' As [Insert]
END CATCH

SELECT *
FROM CardsTable

结果：

Insert
Failed

CardID  PersonID    Number
1       10          22
2       10          22
3       11          24
4       11          24
5       10          22

Answer 2

您应该在表格上实现“插入”和“更新”的触发器，如下所示：

 Create trigger trigger_cardstable_insert on cardstable
 after insert
 as
 Begin
 set nocount on;
 if (select count(c.personid) from cardstable c inner join inserted i on i.personid group by i.personid, c.number) > 1
  Begin

      Delete cardstable
      From cardstable c inner join inserted i on i.cardid = c.cardid
 End
 End

对于更新，它会有所不同，您需要再添加一个条件：

 Create trigger trigger_cardstable_update on cardstable
 after update
 as
 Begin
 set nocount on;
 if update(number) and personid(select count(c.personid) from cardstable c inner join inserted i on i.personid group by i.personid, c.number) > 1
  Begin

      Delete cardstable
      From cardstable c inner join inserted i on i.cardid = c.cardid
 End
 End

如何为每个组添加一个字段？

2 个答案: